Chinook Optional School Association (COSA) is a 501(c)3 nonprofit, parent group that supports the students and staff of Chinook Open Optional Program through volunteerism, fundraising, and social opportunities. Family members automatically belong to the association when their child is enrolled in Chinook Open Optional.

Monthly Board of Directors meetings are open to the membership and are held at Chinook Elementary School on the first Thursday of every month 5:45-6:45 pm. Families are encouraged to attend to find out about upcoming events, stay informed about the program, weigh in on decisions, and get to know other parents.